Boron and carbon containing hard cemented materials and their production



2,806,809 Patented Sept. 17, 1957 Fice BORGN AND CARBQN CGNTAINING HCEMENTED MATERIALS AND THEIR PRO- DUCTION Frank W. Glaser, Lakewood,()hio, assignor, by mesne assignments, to the United States of Americaas represented by the Secretary of the Navy No Drawing. ApplicationNovember it), 1955, Serial No. 546,259

12 Claims. (Cl. 106-43) This invention relates to hard materials orcomposition of matter, and to the production thereof. The hard materialsof the invention are useful for cutting edge elements or cutting pointsof cutting tools, for dies, for providing wear-resistant surfaces, andfor other applications requiring structural material combining strength,hardness, toughness, and resistance to deformation at high temperaturesand pressures. This application is a continuation in part of theapplication of Frank W. Glaser for improvements in Boron Containing HardCemented Materials and Their Production, Serial No. 170,243, filed June24, 1950.

Cemented hard metal carbides produced by powder metallurgy techniquehave long been recognized as the ideal material for applications such ascutting tools, dies, wear-resistant bodies and the like. The bestcemented carbide tool material generally embodies as constituents,tungsten carbide, or the combination of tungsten carbide with additionof titanium, columbium, or tantalum carbide, or mixtures of solidsolutions thereof, together with an additional cementitious or matrixmetal consisting of cobalt, nickel, or alloys of cobalt or nickel.

In making such hard cemented carbide bodies, it was heretofore generallybelieved that in order to give them desired high mechanical strength itwas essential to use as a cementing addition metals which are ductileand which have a considerably lower melting temeprature than thecarbides.

The present invention is based on the discovery that boron, a substancewhich lacks ductility, and which has not been considered to be a metal,constitutes an unusually effective addition substance for use in lieu ofknown ductile cementing metals of relatively low melting point, such'ascobalt and nickel in making hard cemented carbides.

As is known, the heretofore available cemented hard carbide materialsare subject to what is known as cratering or welding on caused by heatand pressure, and consisting of chips of cut steel or the like adheringto the tool point strong enough to pull out carbide grains. It has alsolong been recognized that these deficiencies could be materially reducedby increasing the heat conductivity of such carbide tool material.

More specifically, the present invention is based on the discovery thathard cemented carbides combining known hard metal carbide constituents,with an addition of boron has all the desired characteristics of thebest prior cemented hard metal carbides, with the additional advantageof much greater heat conductivity and much greater corrosion resistance,two factors of critical importance in most of the practical applicationsof cemented carbides.

In general, desirable cemented refractory carbide bodies of theinvention may be produced by combining known hard metal carbideparticles with an addition of boron in proportions varying from about 2%to 50% of the total composition (throughout the present specificationand claims, all proportions are given by weight, unless specificallystated otherwise). However, cemented refractory carbide bodies of theinvention having particularly desirable physical characteristics areobtained by confining the proportions of the addition substance to amore limited range, to Wit, to from about 10% to 20% of the totalcomposition, the balance being formed of the refractory carbideparticles.

Another distinct phase of the present invention is based on thediscovery that boron is also an efiective addition substance for use inmaking hard cemented bodies out of fine particles of availablesilicides, nitrides, and oxides of the metals of the fourth to sixthgroups of the periodic system.

Since the electrical conductivity characteristics closely parallel theheat conductivity characteristics of the substance involved, but aremore accurately measured, the electrical conductivity, or rather itsinverse, the electrical resistivity, will be used as the basis ofcomparison of the carbides referred to herein throughout thespecification and claims. In other words, carbide materials having highheat conductivity have also high electrical conductivity, and viceversa. Thus, by way of comparison, whereas a typical prior art cementedtungsten carbide material has electrical resistivity of aboutmicr0hm-cm., a typical cemented carbide material of the presentinvention has electrical resistivity of only about half as high andless, and a correspondingly greater heat conductivity.

Furthermore, cemented carbide material of the present invention, usingboron as an addition substance, has a much greater corrosion resistance,in fact greater by a factor of about 20, than the corrosion resistanceof prior art cemented carbides using cobalt and/or nickel as a binderaddition, the corrosion resistance increasing with the increase of theproportion of the boron addition.

It is accordingly an object of the invention to provide hard cementedcarbides combining known hard metal carbide particles with boron as anaddition substance.

It is also a distinct object of the invention to provide hard cementedmaterials or compositions combining an addition of boron with particlesof silicides, nitrides, and oxides, as well as carbides of the metals ofthe fourth to sixth group of the periodic system and systems andmixtures thereof.

The present invention is based on the original discovery thatinproducing hard cemented refractory material or composition of matterhaving desirable characteristics superior to those of cementedcarbides-the borides of titanium, zirconium, vanadium, columbium,tantalum, molybdenum, tungsten, iron, manganese, chromium, and/orsilicon, with or without a further addition of boron, all of which arerefractory substances which lack ductility, and have very high meltingpoints compared to cobalt and nickel, constitute highly effectiveaddition substances for usein lieu of known ductile cementing metals,such as cobalt and nickel, having relatively low melting points.

More particularly, the present invention is based on the discovery thatdesired cemented refractory bodies may be obtained by combiningparticles of known carbides of titanium, zirconium, vanadium, columbium,tantalum, molybdenum, tungsten, iron, manganese, chromium, and/orsilicon, or mixtures of solid solutions of these carbides, with anaddition or additions of particles of borides of titanium, zirconium,vanadium, columbium, tantalum, molybdenum, tungsten, iron, manganese,chromium, and/or silicon,v without or with a further addition of boronparticles, and that such cemented bodies constitute a system in whichits chemical constituents are combined in a unique way responsible forthe superior properties of such bodies.

In general, desirable cemented materials of the invention may be made bycombining particles of the refractory metal carbide and with arefractory metal boride addition,"with or without an addition of boron,into a cemented body system in which carbon constitutes from 0.2% to25%, boron from 0.5% to 40%, and the metal from 50% to 90% of the bodycomposition. These proportions correspond to a mixture of carbideparticles which form 98% to 45% of the total mass, with boride particleswhich form 2% to 55% of the total mass. I'f aboron addition, inproportion of 2% to 25% of the total is used, the total of the boron andboride addition should preferably be limited to about 25% of the totalmass of the composition.

Cemented bodies having particularly desirable physical characteristicsare obtained in accordance with the inventionby combining particles oftherefractory metal carbide and the refractory metal boride, with. orwithout an addition of boron, into a cementedbody system in which carbonconstitutes from. 3%. to 12%, boron from 15% to 35%, and the metal fromabout 50% to 90% of the body composition. These proportions correspondto a mixture of 95% to 70% of'carbideparticles with the balance of theboride, without and with the boron addition.

A unique characteristic'of' the cemented bodies of the present inventionis the fact that they exhibit much greater heat conductivity than knowncemented refractory carbides, in which the hard refractory carbideparticles are cemented by the known ductile cementing metals, such ascobalt and nickel having a relatively low melting point. Since the morereadily measured electrical conductivity characteristics closelyparallel the heat conductivity characteristics of the substanceinvolved, but are more accurately measured, the electrical conductivity,or rather its inverse, the electrical resistivity, will be used as. abasis for comparison of the lower cemented bodies referred to hereinthroughout the specification and claims. In other words, cementedcarbides having high heat conductivity, have also high electricalconductivity, or vice versa. Thus,

by Wayof comparison, whereas typical, prior art cemented tungstencarbide materialhas electrical resistivity of about 100 microhms-cm., incontrast, a typical cemented refractory material of the presentinvention has. electrical resistivity of only about half as high and. acorrespondingly greater heat conductivity.

X-ray analysis shows that when particles of the carbides referred toabove are combined withp'articles of a metal boride or borides referredto above without any addition of free boron, the application of heat andpressure to. the mixture of the carbide and. boride particles results inthe formation of a cemented. body in which the carbide and borideingredients of the mixture of particles are present in substantially thesame proportion as in the original mixture of difierent powderparticles.

On the other hand, X-ray analysis shows when particles of the carbidesreferred to above are combined with particles of the borides referred toabove, together with further addition of unbound or free boron, theapplication of heat and pressure to the mixture'of the carbide, borideand boron particles results in the decomposition of the carbideingredients: and the formation of boride with the carbide-formingsubstance or substances in proportion tothe boron present in the total.ingredients of the mass of mixed powder particles. More particularly,X-ray analysis shows that the presenceof unbound or free boron in amixture of carbide particlessubjected to pressure and heat results inthe decomposition of carbide ingredients chromium, and/or silicon, ormixtures of solid solutions of these carbides, with an addition oradditions of particles of borides of titanium, zirconium, vanadium,columbium, tantalum, molybdenum, tungsten, iron, manganese, chromium,and/ or silicon.

A further object of the invention is hard cemented refractory bodiescombining particles of known carbides of titanium, zirconium, vanadium,columbium, tantalum, molybdenum, tungsten, iron, manganese, chromium,and/or silicon, or mixtures of solid solutions of these carbides, withan addition or additions of particles of borides of titanium, zirconium,vanadium, columbium, tantalum, molybdenum, tungsten, iron, manganese,chromium, and/ or silicon with a further addition of boron, so as toform acemented particle system of the elemental constituents of theseveral ingredients, thereby giving the resulting cemented bodyrelatively high heat conductivity and electrical conductivity, and acorrespondingly low electrical resistivity.

The foregoing and other objects of the invention will be best understoodfrom the following detailed description of exemplifications thereof. I

In producing cemented hard carbide materials of the invention, it isimportant that the hard carbide particles should be comminuted to agreat degree of fineness, such as an average particle size of 1 to 2microns, and that the comminution of the carbide'particles should beefiected under conditions which prevent oxidation of the particles.v Ifthe carbide particles are of a size materially larger than about 3microns, such. as 5 microns or more, the cemented carbide material issomewhat poorer in its physical characteristics. Carbide powders ofdesired particles size may be produced from a larger size powder, suchas mesh to -20 mesh powder, by ball-milling to sizeunder an oxidationsuppressing cover of a bath of saturated hydrocarbons, such as mineraloil within an atmos'- phere of inert gas, such as argon, maintained inthe mill spaces under a positive pressure.

It is desirable that all ball-milling should be carried on in a millhaving an interior surface or lining and balls of the same compositionas an ingredient of the milled particles. If a steel mill and steelballs aroused, the ferrous impurities should be -removed after themilling by a treatment such as leaching with sulphuric acid diluted:with. water in concentration between 1:20. to 1:40. Before leaching theball-milled powder should becleaned; of oil by diluting it and washingwith an agent such as ether,,ace= tone, or alcohol, followed byfiltering.

The milled powder: from which the ferrous. particles. have been removedis thenwashed witha volatile agent, such as alcohol or ether, and dried.

The fine dried carbide powder isthen mixed: with the boron addition toprovidev a uniformL intimatemixtureof the metal carbide particles withthe boron addition. Since.-

boron is extremely hard, it likewise should be reduced to a line sizesuch as about 2 microns or less, before: it is: mixed with the line hardcarbide particles. The boron. may be comminuted to size by ball-millingin a manner analogous to the comminution of the carbide particles.

The desired intimatev mixture of the, carbide particles and the boronaddition particles may be secured; by

subjecting the powder mixture to ball-milling for a sufficient length oftime, such as 4 to IOOhours depending" on design and dimensions of theball-mill.

The desired ball-milling to mix is eifectedin a ball-- mill under anoxidation suppressing cover, such asab'ath of purified mineral oil, andan. atmosphere of argon; The oil is then removed from the ball-milledpowder mixture, and the fineparticle mixture is leached, washed anddried with a volatile agent such as alcohol. The ball-milling operationfor reducing the carbide particles andfor effooting the mixture of thecarbide particles with the addition substance may be carried on within abath of water, instead of mineral oil, in which case, however, theingpowder mixture will exhibit poorerpropertiesr Out of the intimatemixture of fine carbide particles and boron addition particles, thedesired cemented material or body is made by compacting and sinterng. Avery effective way for producing the desired shaped bodies out of suchpowder mixtures is by hot-pressing the powder mixture at a temperatureof from 1200 to 2500 C. with pressures from .5 to 3.5 t. s. i. (tons persquare inch). By hot-pressing such powder mixtures with graphite dies,the sintered particles are maintained in an atmosphere consistingpredominantly of carbon dioxide, thus pr serving them against oxidation.it is believed that for best results, the sintering should be carried onat a temperature at which a liquid phase may be expected, so that thesintering or combined pressing and sintering takes place in the presenceof a liquid phase. To simplify the hot-pressing treatment, it may bepreceded by coldpressing the powder mixture in the die, in which it isthereafter hot-pressed.

The graphite dies should not be too hard in order to avoid theircracking. By subjecting the powder mixture to successive compacting andsintering treatment at successively higher temperatures, cementedcarbide material of extremely high strength, toughness, density andhardness may be produced. In order to improve the physicalcharacteristics of the hot-pressed cemented refractory carbide body itmay be subjected to a similar additional sinteiing treatment within aprotective atmosphere, such as purified hydrogen, or purified crackedammonia for shorter or longer periods such as about one-half to severalhours.

In producing a cemented body out of particles of different carbides, theinitial or follow-up sintering treatments may be carried on for asufiicient length of time, and at sufficiently high temperatures tocause the different metal carbides of the different particles tomutually iffuse, and form solid solutions of the different carbides,particularly if the sintering is carried on at a temperature at which aliquid phase exists.

Sintered cemented carbide bodies of the invention may also be producedby first cold-pressing the fine powder mixture into a green compact witha pressure from about 1 to about 35 t. s. i., followed by sintering in anonoxidizing, non-carburizing atmosphere, such as purified hydrogen, orpurified cracked ammonia, at a temperature from about l800 to 2400 C.for about one-half to twelve hours, or more.

The various known refractory hard carbides made by known processes aresuitable for cemented refractory compositions of the invention. Morespecifically, the carbides of titanium, zirconium, columbium,molybdenum, tungsten, tantalum, iron, manganese, chromium and siliconare suitable for combining with a boron addition into a cemented body inaccordance with the principles of the invention.

Because of their high heat conductivity, the present invention makes itpossible to produce very effective hard refractory cemented carbidecompositions with carbides of metals, such as titanium and zirconium,which are available in great abundance, as distinguished from theheretofore generally used cemented tungsten carbides which arerelatively difficult to procure. Accordingly, because of their practicalsignificance there will now be described specific examples of thepractice of the invention, applied to the production of cementedtitanium combined with boron as an addition substance.

A mixture of 85% titanium carbide powder (titanium with 19.3% combinedcarbon), together with an addition of 15 boron powder was hot-pressedwith 3.5 t. s. i. at a temperature of 2400 C. The resulting body had thefollowing characteristics: Modulus of rupture 130,000 to 140,000 p. s.i.; Rockwell A hardness 91; density 4.7 to 4.8 g./cc.; resistivity, 35to 40 microhms-cm.

A similarly produced body of the same composition and hot-pressed with apressure of .5 t. s. i., had the following characteristics: Modulus ofrupture, 100,000

r 6 p. s. i.; Rockwell A hardness, 90; density, 4.6 to 4.7 g./cc.;resistivity, 30 to 35 microhms-cm.

Another body prepared in the same manner with a mixture of titaniumcarbide powder (titanium combined with 19.3% combined carbon) and 15%cobalt boride hot-pressed with 1.5 t. s. i. at 2250 C. had substantiallythe same physical characteristics as example containing 15% boron.

As another example, a powder mixture of titanium carbide and 15% boron,was successively hot-pressed with a pressure of 1.5 t. s. i., first atan initial temperature of 1200 C., then re-pressed at 140- C., andfinally pressed at 1920 C., yielding a cemented body of the followingcharacteristics: Modulus of rupture, 145,000 p. s. i.; Rockwell Ahardness, 91; density, 4.75 g./cc.; resistivity, 20 to 21.5 microhms-cm.

As a further example, a mixture of titanium carbide (with 19.3 combinedcarbon) and 10% boron was hot-pressed with 3.5 t. s. i. at 2350 C. Theresulting body had the following characteristics: Modulus of rupture,130,000; Rockwell A hardness, 92; density, 4.65 g./cc.; resistivity, 50microhms-cm.

It will be noted that both of the cemented carbide bodies of theinvention represented by examples given above have an electricalresistivity not exceedingSO microhms-cm., as compared to the best ofheretofore avail able cemented carbides, which had a resistivity of theorder of microhms-cm., and a correspondingly lower heat conductivity.The unusually high electrical conductivity of bodies of the inventionand their correspondingly high heat conductivity, greatly reduces theirtendency for welding on or cratering when used as a cutting tool, and insimilar applications requiring a material of high hardness, toughness,and resistance to wear under a great pressure and at high temperature.

Cemented bodies of zirconium carbide and of other known refractorycarbides, made with an addition of boron in the same way as the examplesdescribed above have improved physical characteristics of the sameorder.

Furthermore, by similar procedures, fine particles of the silicides,nitrides, and oxides of the metals of the fourth to sixth group of theperiodic system may be mixed with an addition of boron in proportionsvarying from about 5% to 50% of the total body, and formed into cementedbodies of improved physical characteristics.

When a mixture of the refractory carbide particles with the addition ofboron powder particles is subjected to the compacting and sinteringtreatment to produce cemented refractory bodies of the invention, suchas represented by the examples given above, liquid phases are formedduring sintering at high temperatures, and the resulting cemented bodymay not actually constitute a composition containing the mixture of theoriginal ingredients out of which it was formed, but rather a systemcombining the constituents of the refractory carbide particles and theboron addition of the body, bound in a unique way which is effective ingiving it unusual physical characteristics. Thus, by way of example, incase of the cemented refractory body of the invention produced out of amixture of titanium carbide powder particles and boron powder particleshot-pressed with a pressure of 3.5 t. s. i. at a temperature of 2400 C.,it constitutes a system of titanium, carbon and boron in which theseconstituents are present in proportions corresponding to the mixture ofthe titanium carbide particles and boron particles out of which suchcemented refractory body was formed.

Cemented refractory carbide bodies of the invention having generallydesirable characteristics similar to those illustrated by the examplesgiven above, may be made by combining Zirconium carbide or other knownrefractory carbides with the addition of boron in proportions from 5% to50% of the total composition of the body in the manner described above.Cemented refractory bodies iof the invention having particularlydesirable char acteristics are obtained by confining the additionsubstance; boron; to -a-more limited range of proportions, tow1t,-tofrom10% to 20% of the total composition of the cemented refractory carbidebody, the'balance being formedof refractory carbide particles.

Cemented refractory carbide particles made with known cementing metalssuch as with -to 15% cobalt and/or-nickel T acquire greatly improvedphysical characteristics by combiningwith theingredients ofsuch'bodies-2%-to 15%"boron by adding and mixing the boron in powder formwith thecarbide. powder particles'and th'e nickel and/ or cobalt powderparticles prior to compactingand-sintering: However, whencombining-thecarbides-With the boronaddition, as'well'as with combining with'a boronaddition into hard cemented bodies-of the-invention areth'e silicides ofmolybdenum, titanum, zirconium, vanadium, chromiurn'and tungsten.AmongJthe nitrides suitable forcombining with a boron addition into hardcemented bodies of the invention, are the-nitrides-of titanium,zirconium, columbium, vanadium, tantalum. Among the'oxides suitable forcombinin'g"with a boron addition-into hard cemented bodies of theinvention are the oxides of aluminum, titanium, zirconium, tantalum,columbium, magnesium, manganese, vanadium; and silicon By way ofexample, a mixture of fine particles of about 90 molybdenum disilicide'with boron, hot pressed with-3.5t. s. i.- at a temperature of 2400 C.,

yieldeda hard cemented bodyhaving adensity of about 5.8 ge/cc,electricalresistivityof about 30 microhmema, and otherphysical'characteristics of'th'esame order asth'e cemented carbidebodies of the examples of the invent-ion-= given above. As a similarcemented body madewith 85 molybdenum-disilicide, balance boron,

had adensit y-of'about 5 -g.-/cc., other resistivity of about 40microhm:-cm. and generallysimilarother characteristics; A similarcementedbody made With 80% molybdenumdisilicide, balance boron, hada'density of about 5 gt/co, a resistivity of 55.5 microhm-cm. and,generall-y. similar other physical characteristics. Suchcemented-"molybdenum disilicidebodies of the invention had :alsogreathot strength at temperatures of 1000 C.

andiabove and exhibited resistance to corrosion within;

oxidizing atmospheres andcombustion gases at high temperatures of 1000C. and above.

The novel principles of the invention described above will suggestvarious modifications thereof and it is accordingly desired that theinvention shall not-be limited to: any of the exemplifications describedabove.

l. A'=h'ard body consisting essentially of from 50% to 80% of at leastonecarbide of a substance selected from the group consisting oftitanium, zirconium, molybdenum,

tungstemniranadium, chromium, niobium, tantalum' and silicontand*-.20%to 50% of:boron, all proportions-being a 8' by Weight, the carbideingredients'of said body being bound'by' a -solidified-liquid'phasecontaining at least some of its boron content;

2. In the method, of manufacturing hard material, the procedure ofproviding an intimate mixture ofparticles of a major ingredientconsisting of at'least one carbide of a substance selected from the.group consisting of titanium, zirconium, molybdenum, tungsten,vanadium, chromium, niobium, tantalum and silicon 'with additionalingredients consisting essentially of boron so that the lowertemperature said particles form a solid f material constituting a systemcombining the chemical, elements out of which said ingredients areconstituted in proportions in Which they are present in saidingredients.

3. A material as claimedinclaim 1, the major ingredient consistingessentially of titanium carbide.

4. A material 'as claimed in claim 1, boron constituting about 10 to 20%by weight .of the compositiom 5; A material as claimed in claim 1; thema or ingredient consisting essentially of zirconium carbide,boronconstituting about 10 to 20% by weight of the compo sition. v

6. Amaterial as claimed in claim 1, the major ingredient consistingessentially of chromium carbide, boron constituting about 10 to 20% byWeight of the compositron.

7. A material as claimed in claim 1, the major ingredient consistingessentially of silicon carbide, boron constituting about 10 to 20% byweight of the composition.

8. The method of manufacturing solid material as claimed in claim'2, themixture "that is being compacted and heated containing about to 50% byweight of the carbide and about 10 to 20% by Weight of boron.

9. The method of manufacturing, solid material as claimed in claim 2,the mixture that is being compacted and heated containing titaniumcarbide in an amount of 80% to 50% and boron in an amount of about 10%to 20% of the total weight of the mixture.

10. The method of manufacturing solid material as claimediin claim'2,.the mixture that is being compacted and heated containingzirconiumcarbide as the major ingredient, and boron in an amount ofabout 10% to 20% of the total weight of the mixture;

11. The method of manufacturing solid material as claimed in claim .2,the mixture that is being compacted and heated containingchromium.carbide as the major ingredient, and boron in an amount ofabout 10% to 20% of the total Weight of the mixture.

12. The method of manufacturing solid material'as claimed in claiml, themixture that is being compacted and heated containing silicon carbide asthe major ingredient, and boron in an amount of about 10% to 20% of thetotal weight-of .the mixture.

References Cited in the file'ofthis patent UNITED STATES PATENTS.

864,723; Bolling Aug. 27, 1907 2,201,150 Boyer et al. May 21, 19402,412,373 Wejnarth Dec. 10,. 1946 2,438,221 Kurtz et' al. Mar; 23,- 1948

1. A HARD BODY CONSISTING ESSENTIALLY OF FROM 50% TO 80% OF AT LEAST ONECARBIDE OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF TITANIUM,ZIRCONIUM, MOLYBDENUM, TUNGSTEN, VANADIUM, CHROMIUM, NIOBIUM, TANTALUMAND SILICON AND 20% TO 50% OF BORON, ALL PROPORTIONS BEING BY WEIGHT,THE CARBIDE INGREDIENTS OF SAID BODY BEING BOUND BY A SOLIDIFIED LIQUIDPHASE CONTAINING AT LEAST SOME OF ITS BORON CONTENT.